Photonic MEMS and structures

ABSTRACT

An interference modulator (Imod) incorporates anti-reflection coatings and/or micro-fabricated supplemental lighting sources. An efficient drive scheme is provided for matrix addressed arrays of IMods or other micromechanical devices. An improved color scheme provides greater flexibility. Electronic hardware can be field reconfigured to accommodate different display formats and/or application functions. An IMod&#39;s electromechanical behavior can be decoupled from its optical behavior. An improved actuation means is provided, some one of which may be hidden from view. An IMod or IMod array is fabricated and used in conjunction with a MEMS switch or switch array. An IMod can be used for optical switching and modulation. Some IMods incorporate 2-D and 3-D photonic structures. A variety of applications for the modulation of light are discussed. A MEMS manufacturing and packaging approach is provided based on a continuous web fed process. IMods can be used as test structures for the evaluation of residual stress in deposited materials.

BACKGROUND

[0001] This is a continuation-in-part of U.S. patent application Ser.No. 08/744,253, filed Nov. 5, 1996, which is a continuation ofInternational Application No. PCT/US95/05358, filed May 1, 1995, whichis a continuation-in-part of U.S. application Ser. No. 08/238,750, filedMay 5, 1994, now issued as U.S. Pat. No. 5,835,255.

[0002] This invention relates to interferometric modulation.

[0003] Interferometric modulators (IMods) modulate incident light by themanipulation of the optical properties of a micromechanical device. Thisis accomplished by altering the device's interferometric characteristicsusing a variety of techniques. IMods lend themselves to a number ofapplications ranging from flat panels displays and optical computing tofiberoptic modulators and projection displays. The differentapplications can be addressed using different IMod designs.

SUMMARY

[0004] In general, in one aspect, the invention features an IMod baseddisplay that incorporates anti-reflection coatings and/ormicro-fabricated supplemental lighting sources.

[0005] In general, in one aspect, the invention features an efficientdrive scheme for matrix addressed arrays of IMods or othermicromechanical devices.

[0006] In general, in one aspect, the invention features a color schemethat provides a greater flexibility.

[0007] In general, in one aspect, the invention features electronichardware that can be field reconfigured to accommodate different displayformats and/or application functions.

[0008] In general, in one aspect, the invention features an IMod designthat decouples the IMod's electromechanical behavior from the IMod'soptical behavior.

[0009] In general, in one aspect, the invention features an IMod designwith alternative actuation means, some one of which may be hidden fromview.

[0010] In general, in one aspect, the invention features an IMod or IModarray that is fabricated and used in conjunction with a MEMS switch orswitch array, and/or MEMS based logic.

[0011] In general, in one aspect, the invention features an IMod thatcan be used for optical switching and modulation.

[0012] In general, in one aspect, the invention features IMods thatincorporate 2-D and 3-D photonic structures.

[0013] In general, in one aspect, the invention features a variety ofapplications for the modulation of light.

[0014] In general, in one aspect, the invention features a MEMSmanufacturing and packaging approach based on a continuous web fedprocess.

[0015] In general, in one aspect, the invention features IMods used astest structures for the evaluation of residual stress in depositedfilms.

DESCRIPTION

[0016]FIG. 1A is a cross-section of a display substrate incorporating ananti-reflection coating and integrated supplemental lighting. FIG. 1Breveals another scheme for supplemental lighting.

[0017]FIG. 2 shows detail of the fabrication process of a micromachinedarc lamp source.

[0018]FIG. 3 illustrates a bias centered driving scheme for arrays ofIMods in a display.

[0019]FIG. 4A is a diagram which illustrates a color display schemebased on the concept of “base+pigment”. FIG. 4B reveals a block diagramof a system that provides for field reconfigurable display centricproducts. FIG. 4C illustrates the concept as applied to ageneral-purpose display-centric product.

[0020]FIG. 5A is a diagram revealing an IMod geometry that decouples theoptical behavior from the electromechanical behavior, shown in theun-actuated state. FIG. 5B shows the same IMod in the actuated state.FIG. 5C is a plot showing the performance of this IMod design in theblack and white state. FIG. 5D is a plot showing the performance ofseveral color states.

[0021]FIG. 6A shows a diagram of an IMod that similarly decouples theoptical behavior from the electromechanical, however the supportstructure is hidden. FIG. 6B shows the same design in the actuatedstate.

[0022]FIG. 7A illustrates an IMod design that utilizes anisotropicallystressed membranes, in one state. FIG. 7B shows the same IMod in anotherstate.

[0023]FIG. 8A is an illustration showing an IMod that relies onrotational actuation. FIG. 8B reveals the fabrication sequence of therotational IMod design.

[0024]FIG. 9A is a block diagram of a MEMS switch. FIG. 9B is a blockdiagram of a row driver based on MEMS switches. FIG. 9C is a blockdiagram of a column driver based on MEMS switches. FIG. 9D is a blockdiagram of a NAND gate based on MEMS switches. FIG. 9E is a blockdiagram of a display system incorporating MEMS based logic and drivercomponents.

[0025]FIG. 10A is a drawing that reveals the structure, fabrication, andoperation of a MEMS switch. FIG. 10B illustrates two alternative switchdesigns.

[0026]FIG. 11A is a drawing that shows examples of mirroring based 2-Dphotonic structure. FIG. 11B is a drawing of a periodic 2-D photonicstructure.

[0027]FIG. 12 is a diagram which revealing an example of a 3-D photonicstructure.

[0028]FIG. 13A is a drawing illustrating an IMod incorporating amirroring structure in the un-actuated state. FIG. 13B is the same IModin the actuated state. FIG. 13C shows an IMod incorporating periodic 2-Dphotonic structure.

[0029]FIG. 14A illustrates and IMod design which acts as an opticalswitch. FIG. 14B shows a variation of this design that acts as anoptical attenuator.

[0030]FIG. 15A is a diagram of an IMod design that functions as anoptical switch or optical decoupler. FIG. 15B illustrates howcombinations of these IMods can act as a N×N optical switch.

[0031]FIG. 16 shows the fabrication sequence for a tunable IModstructure.

[0032]FIG. 17A illustrates how the tunable IMod structure can beincorporated into a wavelength selective switch. FIG. 17B furtherillustrates how the wavelength selective switch may incorporate solidstate devices. FIG. 17C illustrates how bump-bonded components may beintergrated.

[0033]FIG. 18A is a schematic representation of a two-channelequalizer/mixer. FIG. 18B illustrates how the equalizer/mixer may beimplemented using IMod based components.

[0034]FIG. 19 is a diagram illustrating a continuous web-basedfabrication process.

[0035]FIG. 20 illustrates how IMod based test structures may be used astools for stress measurement.

[0036] FIGS. 21A-21C Describe.

Anti-Reflective Coatings

[0037] An attribute of one previously described IMod design (the inducedabsorber design described in U.S. patent application Ser. No.08/554,630, filed on Nov. 6, 1995, and incorporated by reference) is theefficiency of its dark state, in which it can absorb as much as 99.7% oflight which is incident upon it. This is useful in reflective displays.In the described design, the IMod reflects light of a certain color inthe un-actuated state, and absorbs light in the actuated state.

[0038] Because the IMod array resides on a substrate, the potential forabsorption is diminished by the inherent reflection of the substrate. Inthe case of a glass substrate, the amount of reflection is generallyabout 4% across the visible spectrum. Thus, despite the absorptivecapability of the IMod structure, a dark state can only be as dark asthe front surface reflection from the substrate will permit.

[0039] One way to improve the overall performance of an IMod baseddisplay is by the incorporation of anti-reflection coatings (ARcoatings). These coatings can comprise one or more layers of dielectricfilms deposited on the surface of a substrate and are designed to reducethe reflection from that surface. There are many different possibleconfigurations for such films and design and fabrication is a well knownart. One simple film design is a single coating of magnesium fluorideapproximately one-quarter wave thick. Another example utilizes a quarterwave film of lead fluoride deposited on the glass, followed by a quarterwave film of magnesium fluoride, with yet a third example interposing afilm of zinc sulfide between the two.

[0040]FIG. 1A illustrates one way in which an AR coating may beincorporated into an IMod display to improve the performance of thedisplay system. In FIG. 1A, AR coating 100, which, as stated, couldcomprise one or more thin films, is deposited on the surface of glasslayer 102 bonded to glass substrate 106, on the opposite side of whichis fabricated IMod array 108. The presence of AR coating 100 reduces theamount of incident light 109 reflected from the surface by coupling moreof it into the glass layer 102. The result is that more of the incidentlight is acted upon by the IMod array and a darker display state can beobtained when the IMod is operating in the absorptive mode. The ARcoating 100 could also be deposited directly on the surface of glasssubstrate 106 on the side opposite that of the IMod array.

Integrated Lighting

[0041]FIG. 1A also shows how supplemental lighting may be supplied tosuch a display. In this case an array of microscopic arc lamps, 104, isfabricated into glass layer 102. Arc lamps are efficient suppliers oflight. Historically, arc lamps have been fabricated using techniquesrelevant to the fabrication of ordinary light bulbs. A typical versionof such a lamp is described in U.S. Pat. No. 4,987,496. A glass vesselis built, and electrodes, fabricated separately, are enclosed in thevessel. After filling with an appropriate gas, the vessel is sealed.Although such bulbs may be made small, their method of manufacture maynot be suited to the fabrication of large monolithic arrays of suchbulbs.

[0042] Techniques used in the manufacture of micromechanical structuresmay be applied to the fabrication of microscopic discharge or arc lamps.Because of the microscopic size of these “micro-lamps”, the voltages andcurrents to drive them are significantly lower than those required tosupply arc lamps fabricated using conventional means and sizes. In theexample of FIG. 1A, the array is fabricated such that light 113 emittedby the lamps is directed towards the IMod array 108 by an inherentreflector layer 111, which is described below.

[0043]FIG. 2 provides detail on how one such lamp, optimized for a flatpanel display, could be fabricated. The sequence is described asfollows. As seen in step 1, glass layer 200 is etched to form areflector bowl 201 using wet or dry chemical etching. The depth andshape of the bowl are determined by the required area of illuminationfor each lamp. A shallow bowl would produce a broad reflected beamspread while a parabola would tend to collimate the reflected light. Thediameter of the bowl could vary from 10 to several hundred microns. Thisdimension is determined by the amount of display area that can beacceptably obscured from the viewer's perspective. It is also a functionof the density of the array of micro-lamps. Using standard depositiontechniques, e.g., sputtering, and standard photolithographic techniques,a reflector/metal halide layer 204 and sacrificial layer 202 aredeposited and patterned. The reflector/metal halide layer could be afilm stack comprising aluminum (the reflector) and metal halides such asthallium iodide, potassium iodide, and indium iodide. The metal halide,while not essential, can enhance the properties of the light that isgenerated. The sacrificial layer could be a layer such as silicon, forexample.

[0044] Next, electrode layer 206 is deposited and patterned to form twoseparate electrodes. This material could be a refractory metal liketungsten and would have a thickness that is sufficient to providemechanical support, on the order of several thousand angstroms. Thensacrificial layer 202 is removed using a dry release technique. Theassembly (in the form of an array of such lamps) is sealed by bonding toa glass plate like substrate 106 (shown in FIG. 1A) such that thereflector faces the plate. A gas, such as xenon, is used to backfill thecavities, formed by the lamps during the sealing process, to a pressureof approximately one atmosphere. This could be accomplished byperforming the sealing process in an airtight chamber that has beenpreviously filled with Xenon.

[0045] The application of sufficient voltage to the electrodes of eachlamp will result in an electrical discharge, in the gas between the endsof the electrodes, and the emission of light 205 in a direction awayfrom the reflector 204. This voltage could be as low as several tens ofvolts if the gap spacing is on the order of several hundred microns orless. If the electrode material is deposited with minimal stress, thesacrificial layer, 202, will determine the position of the electrodeswithin the bowl. In this case, the thickness is chosen to position thedischarge at the focal point of the bowl. Should there be residualstress, which would cause the electrodes to move when released, thenthickness is chosen to compensate for this movement. In general thethickness will be some fraction of the depth of the bowl, from severalto tens of microns.

[0046] Referring again to FIG. 1A, the light is shown traveling along apath 113. Thus light is emitted towards the IMod array, where it isacted on and subsequently reflected by the array along paths 110,towards interface 107 and the viewer 111.

[0047] The lamps may be fabricated without including the reflector layerso that they may emit light omnidirectionally.

[0048] Lamps fabricated with or without the reflector may be used in avariety of applications requiring microscopic light sources or lightsource arrays. These could include projection displays, backlights foremissive flat panel displays, or ordinary light sources for internal(homes, buildings) or external (automobiles, flashlights) use.

[0049] Referring to FIG. 1B, an alternative supplemental lightingapproach is shown. Light guide 118 comprises a glass or plastic layerthat has been bonded to substrate 112. Light source 116 which couldcomprise any number of emissive sources such as fluorescent tubes, LEDarrays, or the aforementioned micro-lamp arrays, is mounted on oppositesides of the light guide. The light 122 is coupled into the light guideusing a collimator 120 such that most of the light is trapped within theguide via total internal reflection. Scatter pad 124 is an area of thelight guide that has been roughened using wet or dry chemical means. Thescatter pad is coated with a material or thin film stack 126 whichpresents a reflective surface towards substrate 112 and an absorbingsurface towards the viewer 128.

[0050] When light trapped within the guide is incident upon the scatterpad, the conditions for total internal reflection are violated and someportion 129 of the light scatters in all directions. Scattered lightwhich would normally escape into the surrounding medium, i.e. towardsthe viewer, 128, is reflected into substrate 112 due to the presence ofthe reflective side of coating 126. Like the aforementioned micro-lamps,the scatter pads are fabricated in an array, with each pad dimensionedsuch that the portion of the display that it obscures from direct viewis hardly noticeable. While these dimensions are small, on the order oftens of microns, they can provide sufficient supplemental lightingbecause of the inherent optical efficiency of the underlying IMod array114. The shape of the scatter pad may be circular, rectangular, or ofarbitrary shapes which may minimize their perception by the viewer.

Addressing Elements In An Array

[0051] In order to actuate arrays of IMods in a coordinated fashion fordisplay purposes, a sequence of voltages is applied to the rows andcolumns of the array in what is generally known as a “line at a time”fashion. The basic concept is to apply a sufficient voltage to aparticular row such that voltages applied to selected columns causecorresponding elements on the selected row to actuate or releasedepending on the column voltage. The thresholds and applied voltagesmust be such that only the elements on the selected row are affected bythe application of the column voltages. An entire array can be addressedover a period of time by sequentially selecting the set of rowscomprising the display.

[0052] One simple way of accomplishing this is shown in FIG. 3.Hysteresis curve 300 is an idealized representation of the electropticalresponse of a reflective IMod. The x-axis shows applied voltage, and they-axis shows amplitude of reflected light. The IMod exhibits hysteresisbecause, as the voltage is increased past the pull-in threshold, theIMod structure actuates and becomes highly absorbing. When the appliedvoltage is decreased, the applied voltage must be brought below therelease threshold in order for the structure to move back into theun-actuated state. The difference between the pull-in and releasethresholds produces the hysteresis window. The hysteresis effect, aswell as an alternative addressing scheme, is discussed in U.S. patentapplication Ser. No. 08,744,253, filed on Nov. 5, 1996, and incorporatedby reference. The hysteresis window can be exploited by maintaining abias voltage Vbias, at all times, to keep the IMod in whatever state itwas driven or released into. Voltages Voff and Von correspond tovoltages required to actuate or release the IMod structure. The array isdriven by applying voltages to the columns and rows using electronicsknown as column and row drivers. IMods have been fabricated with apullin threshold of 6 volts, and a release threshold of 3 volts. Forsuch a device, typical values for Vbias, Voff, and Von are 4.5 volts, 0volts, and 9 volts respectively.

[0053] In FIG. 3, timing diagram 302 illustrates the kind of waveformsthat may be applied to actuate an array of IMods that exhibit ahysteresis curve resembling curve 300. A total of five voltages, twocolumn voltages and three row voltages, are required. The voltages areselected such that Vcol1 is exactly twice the value of Vbias, and Vcol0is zero volts. The row voltages are selected so that the differencebetween Vsel F0 and Vcol0 equals Von, and the difference between Vsel F0and Vcol1 equals Voff. Conversely, the difference between Vsel F1 andVcol1 equals Von, and the difference between Vsel F1 and Vcol0 equalsVoff.

[0054] The addressing occurs in alternating frames 0 and 1. In a typicaladdressing sequence, data for row 0 is loaded into the column driversduring frame 0 resulting in either a voltage level of Vcol1 or Vcol0being applied depending on whether the data is a binary one or zerorespectively. When the data has settled, row driver 0 applies a selectpulse with the value of Vsel F0. This results in any IMods on columnswith Vcol0 present becoming actuated, and IMods on columns with Vcol1present, releasing. The data for the next row is loaded into the columnsand a select pulse applied to that row and so on sequentially until theend of the display is reached. Addressing is then begun again with row0; however this time the addressing occurs within frame 1.

[0055] The difference between the frames is that the correspondencebetween data and column voltages is switched, a binary zero is nowrepresented by Vcol0, and the row select pulse is now at the level ofVsel F1. Using this technique, the overall polarity of the voltagesapplied to the display array is alternated with each frame. This isuseful, especially for MEMS based displays, because it allows for thecompensation of any DC level charge buildup that can occur when onlyvoltages of a single polarity are applied. The buildup of a chargewithin the structure can significantly offset the electroptical curve ofthe IMod or other MEM device.

Color Display Schemes

[0056] Because the IMod is a versatile device with a variety ofpotential optical responses, a number of different color display schemesare enabled having different attributes. One potential scheme exploitsthe fact that there are binary IMod designs that are capable ofachieving color states, black states, and white states in the same IMod.This capability can be used to achieve a color scheme that can bedescribed as “base+pigment”. This terminology is used because theapproach is analogous to the way in which paint colors are produced byadding pigments to a white base to achieve a desired color. Using thisapproach, a particular paint can attain any color in the spectrum andany level of saturation by controlling the content and amount ofpigments that are added to the base. The same can be said for a displaythat incorporates colored and black and white pixels.

[0057] As shown in FIG. 4A, a pixel 400 comprises five subpixelelements, 402, 404, 406, and 408, with each subpixel capable ofreflecting red, green, blue, and white respectively. All of thesubpixels are capable of a black state. Control over the brightness ofeach subpixel can be accomplished using pulse width modulation relatedtechniques as discussed in U.S. Pat. No. 5,835,255. In conjunction withproperly selected relative subpixel sizes, this results in a pixel overwhich a very large degree of control can be exercised of brightness andsaturation. For example, by minimizing the overall brightness of thewhite subpixels, highly saturated colors may be achieved. Conversely, byminimizing the brightness of the color subpixels, or by maximizing themin conjunction with the white subpixels, a bright black and white modemay be achieved. All variations in between are obviously attainable aswell.

User Control of Color Scheme

[0058] The previously described color scheme, as well as the inherentattributes of an IMod-based display in terms of resolution, gray scaledepth, and refresh rate, provides flexibility in display performance.Given this range, it is useful to give the user of a product containingsuch a display control over its general characteristics. Alternatively,it may be advantageous for the display to automatically adapt todifferent viewing needs.

[0059] For example, a user may want to use a product in black and whitemode if, some context, only text were being viewed. In anothersituation, however, the user may want to view high quality color stillimages, or in yet another mode may want to view live video. Each ofthese modes, while potentially within the range of a given IMod displayconfiguration, requires tradeoffs in particular attributes. Tradeoffsinclude the need for low refresh rates if high-resolution imagery isrequired, or the ability to achieve high gray scale depth if only blackand white is requested.

[0060] To give the user this kind of on demand flexibility, thecontroller hardware may be reconfigurable to some extent. Tradeoffs area consequence of the fact that any display has only a certain amount ofbandwidth, which is fundamentally limited by the response time of thepixel elements and thus determines the amount of information which canbe displayed at a given time.

[0061] One display architecture that could provide such flexibility isillustrated in FIG. 4B. In this block diagram, controller logic 412 isimplemented using one of a variety of IC technologies, includingprogrammable logic devices (PLAs) and field programmable gate arrays(FPGAs), which allow for the functionality of the component to bealtered or reconfigured after it leaves the factory. Such devices, whichare traditionally used for specialized applications such as digitalsignal processing or image compression, can provide the high performancenecessary for such processing, while supplying flexibility during thedesign stage of products incorporating such devices.

[0062] The controller 412 provides signals and data to the driverelectronics 414 and 416 for addressing the display 418. Conventionalcontrollers are based on IC's or Application Specific IntegratedCircuits (ASICs), which are effectively “programmed” by virtue of theirdesign during manufacture. The term program, in this case, means aninternal chip layout comprising numerous basic and higher level logicalcomponents (logic gates and logic modules or assemblies of gates). Byusing field programmable devices such PLAs or FPGAs, different displayconfigurations may be loaded into the display controller component inthe form of hardware applications or “hardapps”, from a component 410,which could be memory or a conventional microprocessor and memory. Thememory could be in the form of EEPROMS or other reprogrammable storagedevices, and the microprocessor could take on the form of simplemicrocontroller whose function is to load the hardapp from memory intothe FPGA, unless this were performed by whatever processor is associatedwith the general functioning of the product. This approach isadvantageous because with relatively simple circuitry it is possible toachieve a wide variety of different display performance configurationsand mixed display scan rates, along with the potential to combine them.

[0063] One portion of the screen, for example, might be operated as alow-resolution text entry area, while another provides high qualityrendition of an incoming email. This could be accomplished, within theoverall bandwidth limitations of the display, by varying the refreshrate and # of scans for different segments of the display. Thelow-resolution text area could be scanned rapidly and only once or twicecorresponding to one or two bits of gray scale depth. The high renditionemail area could be scanned rapidly and with three or four passescorresponding to three or four bits of grayscale.

Configurable Electronic Products

[0064] This idea may be generalized to include not just thefunctionality of the display controller, but also the functionality ofthe overall product. FIG. 4C shows a configuration of a generic portableelectronic product 418 that has a programmable logic device orequivalent at its core 420. In many display centric personal electronicproducts, such as PDAs (personal digital assistants) and electronicorganizers, the central processor is a variant of a RISC processor thatuses a reduced instruction set. While RISC processors are more efficientversions of CPUs that power most personal computers, they are stillgeneral-purpose processors that expend a lot of energy performingrepetitive tasks such as retrieving instructions from memory.

[0065] In personal computers, power consumption is not an issue, and theuser typically wants to run a large number of complicated softwareapplications. The opposite is true of typical display centric/personalelectronic products. They are required to consume low power and offer arelatively small number of relatively simple programs. Such a regimefavors implementing the special purpose programs, which could includeweb browsers, calendar functions, drawing programs, telephone/addressdatabases, and handwriting/speech recognition among others, as hardapps.Thus whenever a particular mode of functionality, e.g., a program, isrequired by the user, the core processor is reconfigured with theappropriate hardapp and the user interacts with the product. Thus thehardapp processor, a variant of a Field Programmable Gate Array has thehardapp (i.e. program) manifested in its internal logic and connections,which get re-arranged and re-wired every time a new hardapp is loaded.Numerous suppliers of these components also provide an applicationdevelopment system that allows a specialized programming language (ahardware description language) to be reduced into the logicalrepresentation that makes up the appropriate processor. Numerous effortsare also underway to simplify the process or reducing higher levelprogramming languages into this form as well. One approach to realizingsuch a processor is detailed in the paper Kouichi Nagami, et al,“Plastic Cell Architecture: Towards Reconfigurable Computing forGeneral-Purpose”, Proc. IEEE Workshop on FPGA-based Custom ComputingMachines, 1998.

[0066] Referring again to FIG. 4C, the hardapp processor 420 is shown atthe center of a collection of I/O devices and peripherals that it willutilize, modify, or ignore based on the nature and function of thehardapp currently loaded. The hardapps can be loaded from memory 422resident in the product, or from an external source via RF or IRinterface, 424, which could pull hardapps from the internet, cellularnetworks, or other electronic devices, along with content for aparticular hardapp application. Other examples of hardapps include voicerecognition or speech synthesis algorithms for the audio interface 432,handwriting recognition algorithms for pen input 426, and imagecompression and processing modes for image input device 430. Such aproduct could perform a myriad of functions by virtue of its majorcomponents, the display as the primary user interface and thereconfigurable core processor. Total power consumption for such a devicecould be on the order of tens of milliwatts versus the several hundredmilliwatts consumed by existing products.

Decoupling Electromechanical Aspects From Optical Aspects

[0067] U.S. patent application Ser. Nos. 08/769,947, filed on Dec. 19,1996, and 09/056,975 filed on Apr. 4, 1998, and incorporated byreference, have described IMod designs that propose to decouple theelectromechanical performance of an IMod from its optical performance.Another way in which this may be accomplished is illustrated in FIGS. 5Aand 5B. This design uses electrostatic forces to alter the geometry ofan interferometric cavity. Electrode 502 is fabricated on substrate 500and electrically isolated from membrane/mirror 506 by insulating film504. Electrode 502 functions only as an electrode, not also as a mirror.

[0068] An optical cavity 505 is formed between membrane/mirror 506 andsecondary mirror 508. Support for secondary mirror 508 is provided by atransparent superstructure 510, which can be a thick deposited organic,such as SU-8, polyimide, or an inorganic material. With no voltageapplied, the membrane/mirror 506, maintains a certain position shown inFIG. 5A, relative to secondary mirror 508, as determined by thethickness of the sacrificial layers deposited during manufacture. For anactuation voltage of about four volts a thickness of several thousandangstroms might be appropriate. If the secondary mirror is made from asuitable material, say chromium, and the mirror/membrane made from areflective material such as aluminum, then the structure will reflectcertain frequencies of light 511 which may be perceived by viewer 512.In particular, if the chromium is thin enough to be semitransparent,about 40 angstroms, and the aluminum sufficiently thick, at least 500angstroms, as to be opaque, then the structure may have a wide varietyof optical responses. FIGS. 5C and 5D show examples of black and whiteand color responses respectively, all of which are determined by thecavity length, and the thickness of the constituent layers.

[0069]FIG. 5B shows the result of a voltage applied between primaryelectrode 502 and membrane mirror 506. The membrane/mirror is verticallydisplaced thus changing the length of the optical cavity and thereforethe optical properties of the IMod. FIG. 5C shows one kind of reflectiveoptical response which is possible with the two states, illustrating theblack state 521 when the device is fully actuated, and a white state 523when the device is not. FIG. 5D shows an optical response with colorpeaks 525, 527, and 529, corresponding to the colors blue, green, andred respectively. The electromechanical behavior of the device thus maybe controlled independently of the optical performance. Materials andconfiguration of the primary electrode, which influence theelectromechanics, may be selected independently of the materialscomprising the secondary mirror, because they play no role in theoptical performance of the IMod. This design may be fabricated usingprocesses and techniques of surface micromachining, for example, theones described in U.S. patent application Ser. No. 08,688,710, filed onJul. 31, 1996 and incorporated by reference.

[0070] In another example, shown in FIG. 6A, the support structure forthe IMod 606 is positioned to be hidden by the membrane/mirror 608. Inthis way the amount of inactive area is effectively reduced because theviewer sees only the area covered by the membrane/mirror and the minimumspace between adjoining IMods. This is unlike the structure in FIG. 5Awhere the membrane supports are visible and constitute inactive andinaccurate, from a color standpoint, area. FIG. 6B, reveals the samestructure in the actuated state.

[0071] In FIG. 7A, another geometric configuration is illustrated foruse in an IMod structure. This design is similar to one shown in U.S.Pat. No. 5,638,084. That design relied upon an opaque plastic membranethat is anisotropically stressed so that it naturally resides in acurled state. Application of a voltage flattens the membrane to providea MEMS-based light shutter.

[0072] The device's functionality may be improved by making itinterferometric. The IMod variation is shown in FIG. 7A where thin filmstack 704 is like the dielectric/conductor/insulator stack which is thebasis for the induced absorber IMod design discussed in U.S. patentapplication Ser. No. 08/688,710, filed on Jul. 31, 1996 and incorporatedby reference.

[0073] Application of a voltage between aluminum membrane 702 and stack704 causes the membrane 702 to lie flat against the stack. Duringfabrication, aluminum 702, which could also include other reflectivemetals (silver, copper, nickel), or dielectrics or organic materialswhich have been undercoated with a reflective metal, is deposited on athin sacrificial layer so that it may be released, using wet etch or gasphase release techniques. Aluminum membrane 702 is further mechanicallysecured to the substrate by a support tab 716, which is depositeddirectly on optical stack 704. Because of this, light that is incidenton the area where the tab and the stack overlap is absorbed making thismechanically inactive area optically inactive as well. This techniqueeliminates the need for a separate black mask in this and other IModdesigns.

[0074] Incident light 706 is either completely absorbed or a particularfrequency of light 708, is reflected depending on the spacing of thelayers of the stack. The optical behavior is like that of the inducedabsorber IMod described in U.S. patent application Ser. No. 08/688,710,filed on Jul. 31, 1996, and incorporated by reference.

[0075]FIG. 7B shows the device configuration when no voltage is applied.The residual stresses in the membrane induce it to curl up into atightly wound coil. The residual stresses can be imparted by depositionof a thin layer of material 718 on top of the membrane, which hasextremely high residual tensile stress. Chromium is one example in whichhigh stresses may be achieved with a film thickness a low as severalhundred angstroms. With the membrane no longer obstructing its path,light beam 706 is allowed to pass through the stack 704 and intersectwith plate 710. Plate 710 can reside in a state of being either highlyabsorbing or highly reflective (of a particular color or white). For themodulator to be used in a reflective display, the optical stack 704would be designed such that when the device is actuated it would eitherreflect a particular color (if plate 710 were absorbing) or be absorbing(if plate, 710 were reflective).

Rotational Actuation

[0076] As shown in FIG. 8A, another IMod geometry relies on rotationalactuation. Using the processes discussed in U.S. patent application Ser.No. 08/688,710, filed on Jul. 31, 1996 and incorporated by reference,electrode 802, an aluminum film about 1000 angstroms thick, isfabricated on substrate 800. Support post 808 and rotational hinge 810,support shutter 812, upon which a set of reflecting films 813 has beendeposited. The support shutter may be an aluminum film which is severalthousand angstroms thick. Its X-Y dimensions could be on the order oftens to several hundred microns. The films may be interferometric anddesigned to reflect particular colors. A fixed interferometric stack inthe form of an induced absorber like that described in U.S. patentapplication Ser. No. 08/688,710, filed on Jul. 31, 1996 and incorporatedby reference would suffice. They may also comprise polymers infused withcolor pigments, or they may be aluminum or silver to provide broadbandreflection. The electrode 802 and the shutter 812 are designed such thatthe application of a voltage (e.g., 10 volts) between the two causes theshutter 812 to experience partial or full rotation about the axis of thehinge. Only shutter 818 is shown in a rotated state although typicallyall of the shutters for a given pixel would be driven in unison by asignal on the common bus electrode 804. Such a shutter would experiencea form of electromechanical hysteresis if the hinges and electrodedistances were designed such that the electrostatic attraction of theelectrodes overcomes the spring tension of the hinge at some pointduring the rotation. The shutters would thus have twoelectromechanically stable states.

[0077] In a transmissive mode of operation, the shutter would eitherblock incident light or allow it to pass through. FIG. 8A illustratesthe reflective mode where incident light 822 is reflected back to theviewer 820. In this mode, and in one state, the shutter either reflectsa white light, if the shutter is metallized, or reflects a particularcolor or set of colors, if it is coated with interferometric films orpigments. Representative thicknesses and resulting colors, for aninterferometric stack, are also described in U.S. patent applicationSer. No. 08/688,710, filed on Jul. 31, 1996 and incorporated byreference. In the other state, the light is allowed to pass through andbe absorbed in substrate 800 if the opposite side of the shutter werecoated with an absorbing film or films 722. These films could compriseanother pigment infused organic film, or an induced absorber stackdesigned to be absorbing. Conversely, the shutters may be highlyabsorbing, i.e., black, and the opposite side of substrate 800 coatedwith highly reflective films 824, or be selectively coated with pigmentor interferometric films to reflect colors, along the lines of the colorreflecting films described above.

[0078] Operation of the device may be further enhanced by the additionof supplementary electrode 814, which provides additional torque to theshutter when charged to a potential that induces electrostaticattraction between supplementary electrode 814 and shutter 812.Supplementary electrode 814 comprises a combination of a conductor 814and support structure 816. The electrode may comprise a transparentconductor such as ITO that could be about thousand angstroms thick. Allof the structures and associated electrodes are machined from materialsthat are deposited on the surface of a single substrate, i.e.monolithically, and therefore are easily fabricated and reliablyactuated due to good control over electrode gap spaces. For example, ifsuch an electrode were mounted on an opposing substrate, variations inthe surface of both the device substrate and opposing substrate couldcombine to produce deviations as much as several microns or more. Thusthe voltage required to affect a particular change in behavior couldvary by as much as several tens of volts or more. Structures that aremonolithic follow substrate surface variations exactly and suffer littlesuch variation.

[0079]FIG. 8B, steps 1-7, shows a fabrication sequence for therotational modulator. In step 1, substrate 830 has been coated withelectrode 832 and insulator 834. Typical electrode and insulatormaterials are aluminum and silicon dioxide, each of a thickness of onethousand angstroms each. These are patterned in step 2. Sacrificialspacer 836, a material such as silicon several microns in thickness, hasbeen deposited and patterned in step 3 and coated withpost/hinge/shutter material 838 in step 4. This could be an aluminumalloy or titanium/tungsten alloy about 1000 angstroms thick. In step 5,material 838 has been patterned to form bus electrode 844, support post840, and shutter 842. Shutter reflector 846 has been deposited andpatterned in step 6. In step 7, the sacrificial spacer has been etchedaway yielding the completed structure. Step 7 also reveals a top view ofthe structure showing detail of the hinge comprising support posts 848,torsion arm 850, and shutter 852.

Switching Elements

[0080] For IMods that are binary devices only a small number of voltagelevels is required to address a display. The driver electronics need notgenerate analog signals that would be required to achieve gray scaleoperation.

[0081] Thus, the electronics may be implemented using other means assuggested in U.S. patent application Ser. No. 08/769,947, filed on Dec.19, 1996 and incorporated by reference. In particular the driveelectronics and logic functions can be implemented using switch elementsbased on MEMS.

[0082]FIGS. 9A through 9E illustrate the concept. FIG. 9A is a diagramof a basic switch building block with an input 900 making a connectionto output 904 by application of a control signal 902. FIG. 9Billustrates how a row driver could be implemented. The row driver forthe addressing scheme described above requires the output of threevoltage levels. Application of the appropriate control signals to therow driver allows one of the input voltage levels to be selected foroutput 903. The input voltages are Vcol1, Vcol0, and Vbias correspondingto 906, 908, and 910 in the figure. Similarly, for the column drivershown in FIG. 9C, the appropriate control signals result in theselection of one or the other input voltage levels for delivery to theoutput 920. The input voltages are Vsel F1, Vsel F0, and ground,corresponding to 914, 916, and 918 in the figure. FIG. 9D illustrateshow a logic device 932, may be implemented, in this case a NAND gate,using basic switch building blocks 934, 936, 938, and 940. All of thesecomponents can be configured and combined in a way that allows for thefabrication of the display subsystem shown in FIG. 9E. The subsystemcomprises controller logic 926, row driver 924, column driver 928, anddisplay array 930, and uses the addressing scheme described above inFIG. 3.

[0083] Fabrication of the switch elements as MEMS devices makes itpossible to fabricate an entire display system using a single process.The switch fabrication process becomes a subprocess of the IModfabrication process and is illustrated in FIG. 10A.

[0084] Step 1 shows both a side view and top view of the initial stage.Arrow 1004 indicates the direction of the perspective of the side view.Substrate 1000 has had sacrificial spacer 1002 a silicon layer 2000angstroms thick deposited and patterned on its surface. In step 2, astructural material, an aluminum alloy several microns thick, has beendeposited and patterned to form source beam 1010, drain structure 1008,and gate structure 1006. Several hundred angstroms of a non-corrodingmetal such as gold, iridium or platinum may be plated onto thestructural material at this point to maintain low contact resistancethrough the life of the switch. Notch 1012 has been etched in sourcebeam 1010 to facilitate the movement of the beam in a plane parallel tothat of the substrate. The perspective of the drawing is different insteps 3 and 4, which now compare a front view with a top view. Arrows1016 indicate the direction of the perspective of the front view. Instep 3, the sacrificial material has been etched away leaving the sourcebeam 1010 intact and free to move.

[0085] When a voltage is applied between the source beam and the gatestructure, the source beam 1010 is deflected towards gate 1006 until itcomes into contact with the drain 1008, thereby establishing electricalcontact between the source and the drain. The mode of actuation isparallel to the surface of the substrate, thus permitting a fabricationprocess that is compatible with the main IMod fabrication processes.This process also requires fewer steps than those used to fabricateswitches that actuate in a direction normal the substrate surface.

[0086]FIGS. 10B and 10C illustrates two alternative designs for planarMEM switches. The switch in FIG. 10B differs in that switch beam 1028serves to provide contact between drain 1024 and source 1026. In theswitch of FIG. 10A, currents that must pass through the source beam tothe drain may effect switching thresholds, complicating the design ofcircuits. This is not the case with switch 1020. The switch in FIG. 10Creveals a further enhancement. In this case, insulator 1040 electricallyisolates switch beam 1042 from contact beam 1038. This insulator may bea material such as SiO2 that can be deposited and patterned usingconventional techniques. Use of such a switch eliminates the need toelectrically isolate switch drive voltages from logic signals incircuits comprising these switches.

Multidimensional Photonic Structures

[0087] In general, IMods feature elements that have useful opticalproperties and are movable by actuation means with respect to themselvesor other electrical, mechanical or optical elements.

[0088] Assemblies of thin films to produce interferometric stacks are asubset of a larger class of structures that we shall refer to asmultidimensional photonic structures. Broadly, we define a photonicstructure as one that has the ability to modify the propagation ofelectromagnetic waves due to the geometry and associated changes in therefractive index of the structure. Such structures have a dimensionalaspect because they interact with light primarily along one or moreaxes. Structures that are multidimensional have also been referred to asphotonic bandgap structures (PBG's) or photonic crystals. The text“Photonic Crystals” by John D. Joannopoulos, et al describes photonicstructures that are periodic.

[0089] A one-dimensional PBG can occur in the form of a thin film stack.By way of example, FIG. 16 shows the fabrication and end product of anIMod in the form of a dielectric Fabry-Perot filter. Thin film stacks1614 and 1618, which could be alternating layers of silicon and silicondioxide each a quarter wave thick, have been fabricated on a substrateto form an IMod structure that incorporates central cavity 1616. Ingeneral, the stack is continuous in the X and Y direction, but has aperiodicity in the optical sense in the Z direction due to variations inthe refractive index of the material as they are comprised ofalternating layers with high and low indices. This structure can beconsidered one-dimensional because the effect of the periodicity ismaximized for waves propagating along one axis, in this case the Z-axis.

[0090]FIGS. 11A and 11B illustrate two manifestations of atwo-dimensional photonic structure. In FIG. 11A, a microring resonator1102 can be fabricated from one of a large number of well knownmaterials, an alloy of tantalum pentoxide and silicon dioxide forexample, using well known techniques. For a device optimized forwavelengths in the 1.55 um range, typical dimensions are w=1.5 um, h=1.0um, and r=10 um.

[0091] Fabricated on a substrate 1100 (glass is one possibility thoughthere are many others), the structure is essentially a circularwaveguide whose refractive index and dimensions w, r, and h determinethe frequencies and modes of light which will propagate within it. Sucha resonator, if designed correctly, can act as a frequency selectivefilter for broadband radiation that is coupled into it. In this case,the radiation is generally propagating in the XY plane as indicated byorientation symbol 1101. The one-dimensional analog of this device wouldbe a Fabry-Perot filter made using single layer mirrors. Neither deviceexhibits a high order optical periodicity, due to the single layer“boundaries” (i.e. mirrors); however, they can be considered photonicstructures in the broad sense.

[0092] A more traditional PBG is shown in FIG. 11B. Columnar array 1106presents a periodic variation in refractive index in both the X and Ydirections. Electromagnetic radiation propagating through this medium ismost significantly affected if it is propagating within the XY plane,indicated by orientation symbol 1103.

[0093] Because of its periodic nature, the array of FIG. 11B sharesattributes with a one-dimensional thin film stack, except for itshigher-order dimensionality. The array is periodic in the sense thatalong some axis through the array, within the XY plane, the index ofrefraction varies between that of the column material, and that of thesurrounding material, which is usually air. Appropriate design of thisarray, utilizing variations on the same principles applied to the designof thin film stacks, allows for the fabrication of a wide variety ofoptical responses, (mirrors, bandpass filters, edge filters, etc.)acting on radiation traveling in the XY plane. Array 1106 in the caseshown in FIG. 11B includes a singularity or defect 1108 in the form of acolumn that, differs in its dimension and/or refractive index. Forexample, the diameter of this column might be fractionally larger orsmaller than the remaining columns (which could be on the order of aquarter wavelength in diameter), or it may be of a different material(perhaps air vs. silicon dioxide). The overall size of the array isdetermined by the size of the optical system or component that needs tobe manipulated. The defect may also occur in the form of the absence ofa column or columns (a row), depending on the desired behavior. Thisstructure is analogous to the dielectric Fabry-Perot filter of FIG. 16,but it functions in only two dimensions. In this case, the defect isanalogous to the cavity, 1616. The remaining columns are analogous tothe adjacent two-dimensional stacks.

[0094] The relevant dimensions of the structure of FIG. 11B are denotedby column x spacing sx, column y spacing sy, (either of which could beconsidered the lattice constant), column diameter d, and array height,h. Like the quarter wave stack, the one-dimensional equivalent, columndiameters and spacings can be on the order of a quarter wave. Theheight, h, is determined by the desired propagation modes, with littlemore than one half wavelength used for single mode propagation. Theequations for relating the size of the structures to their effect onlight are well known and documented in the text “Photonic Crystals” byJohn D. Joannopoulos, et al.

[0095] This kind of structure may also be fabricated using the samematerials and techniques used to fabricate the resonator 1102. Forexample, a single film of silicon may be deposited on a glass substrateand patterned, using conventional techniques, and etched using reactiveion etching to produce the high aspect ratio columns. For a wavelengthof 1.55 um, the diameter and spacing of the columns could be on theorder of 0.5 um and 0.1 um respectively.

[0096] Photonic structures also make it possible to direct radiationunder restrictive geometric constraints. Thus they are quite useful inapplications where it is desirable to redirect and/or select certainfrequencies or bands of frequencies of light when dimensionalconstraints are very tight. Waveguides, channeling light propagating inthe XY plane, may be fabricated which can force light to make 90 degreeturns in a space less than the wavelength of the light. This can beaccomplished, for example, by creating the column defect in the form ofa linear row, which can act as the waveguide.

[0097] A three-dimensional structure is illustrated in FIG. 12.Three-dimensional periodic structure 1202 acts on radiation propagatingin the XY, YZ, and XZ planes. A variety of optical responses may beattained by appropriate design of the structure and selection of itsconstituent materials. The same design rules apply, however they areapplied three-dimensionally here. Defects occur in the form of points,lines, or regions, vs. points and lines, which differ in size and/orrefractive index from the surrounding medium. In FIG. 12, the defect1204 is a single point element but may also be linear or a combinationof linear and point elements or regions. For example, a “linear” or“serpentine” array of point defects may be fabricated such that itfollows an arbitrary three-dimensional path through the PBG, and acts asa tightly constrained waveguide for light propagating within it. Thedefect would generally be located internally but is shown on the surfacefor purposes of illustration. The relevant dimensions of this structureare all illustrated in the figure. The diameter and spacing andmaterials of the PBG are completely application dependent, however theaforementioned design rules and equations also apply.

[0098] Three-dimensional PBGs are more complicated to make. Conventionalmeans for fabricating one-dimensional or two-dimensional features, ifapplied in three dimensions, would involve multiple applications ofdeposition, pattern, and etch cycles to achieve the third dimension inthe structure. Fabrication techniques for building periodicthree-dimensional structures include: holographic, where aphotosensitive material is exposed to a standing wave and replicates thewave in the form of index variations in the material itself;self-organizing organic or self-assembling materials that rely on innateadhesion and orientation properties of certain co-polymeric materials tocreate arrays of columnar or spherical structures during the depositionof the material; ceramic approaches that can involve the incorporationof a supply of spherical structures of controlled dimensions into aliquid suspension that, once solidified, organizes the structures, andcan be removed by dissolution or high temperature; combinations of theseapproaches; and others.

[0099] Co-polymeric self-assembly techniques are especially interestingbecause they are both low temperature and require minimal or nophotolithography. In general, this technique involves the dissolution ofa polymer, polyphenylquinoine-block-polystyrene (PPQmPSn) is oneexample, into a solvent such as carbon disulfide. After spreading thesolution onto a substrate and allowing the solvent to evaporate, a closepacked hexagonal arrangement of air filled polymeric spheres results.The process can be repeated multiple times to produce multilayers, theperiod of the array may be controlled by manipulating the number ofrepeat units of the components (m and n) of the polymer. Introduction ofa nanometer sized colloid comprising metals, oxides, or semiconductorsthat can have the effect of reducing the period of the array further, aswell as increasing the refractive index of the polymer.

[0100] Defects may be introduced via direct manipulation of the materialon a submicron scale using such tools as focused ion beams or atomicforce microscopes. The former may be used to remove or add material invery small selected areas or to alter the optical properties of thematerial. Material removal occurs when the energetic particle beam, suchas that used by a Focused Ion Beam tool, sputters away material in itspath. Material addition occurs when the focused ion beam is passedthrough a volatile metal containing gas such as tungsten hexafluoride(for tungsten conductor) or silicon tetrafluoride (for insulatingsilicon dioxide). The gas breaks down, and the constituents aredeposited where the beam contacts the substrate. Atomic force microscopymay be used to move materials around on the molecular scale.

[0101] Another approach involves the use of a technique that can becalled micro-electrodeposition and which is described in detail in U.S.Pat. No. 5,641,391. In this approach a single microscopic electrode canbe used to define three-dimensional features of submicron resolutionusing a variety of materials and substrates. Metal “defects” depositedin this way could be subsequently oxidized to form an dielectric defectaround which the PBG array could be fabricated using the techniquesdescribed above.

[0102] The existence of surface features, in the form of patterns ofother materials, on the substrate upon which the PBG is fabricated mayalso serve as a template for the generation of defects within the PBGduring its formation. This is particularly relevant to PBG processesthat are sensitive to substrate conditions, primarily self-assemblyapproaches. These features may encourage or inhibit the “growth” of thePBG in a highly localized region around the seed depending on thespecific nature of the process. In this way, a pattern of defect “seeds”may be produced and the PBG formed afterwards with the defects createdwithin during the PBG formation process.

[0103] Thus, the class of devices known as IMods may be furtherbroadened by incorporating the larger family of multidimensionalphotonic structures into the modulator itself. Any kind of photonicstructure, which is inherently a static device, may now be made dynamicby altering its geometry and/or altering its proximity to otherstructures. Similarly, the micromechanical Fabry-Perot filter (shown inFIG. 16), comprising two mirrors which are each one-dimensional photonicstructures, may be tuned by altering the cavity width electrostatically.

[0104]FIG. 13 shows two examples of IMod designs incorporatingtwo-dimensional PBGs. In FIG. 13A, a cutaway diagram reveals aself-supporting membrane 1304, which has been fabricated with amicroring resonator 1306 mounted on the side facing the substrate.Waveguides 1301 and 1302 lying within the bulk of the substrate 1303 areplanar and parallel and can be fabricated using known techniques. InFIG. 13A, the IMod is shown in the un-driven state with a finite airgap(number) between the microring and the substrate. The microring isfabricated so that its position overlaps and aligns with the pairedwaveguides in the substrate below. Dimensions of the microring areidentical to the example described above. Crossection 1305 shows thedimensions of the waveguides which could be w=1 um, h=0.5 um, and t=100nm. In the un-driven state, light 1308, propagates undisturbed inwaveguide 1302, and the output beam 1310 is spectrally identical to theinput 1308.

[0105] Driving the IMod to force the microring into intimate contactwith the substrate and waveguides alters the optical behavior of thedevice. Light propagating in waveguide 1302 may now couple into themicroring by the phenomenon of evanescence. The microring, if sizedappropriately, acts as an optical resonator coupling a selectedfrequency from waveguide 1302 and injecting it into waveguide 1301. Thisis shown in FIG. 13B where light beam 1312 is shown propagating in adirection opposite the direction of light 1308. Such a device may beused as a frequency selective switch that picks particular wavelengthsout of a waveguide by the application of a voltage or other drivingmeans required to bring the structure into intimate contact with theunderlying waveguides. A static version of this geometry is described inthe paper B. E. Little, et al, “Vertically Coupled Microring ResonatorChannel Dropping Filter”, IEEE Photonics Technology Letters, vol. 11,no. 2, 1999.

[0106] Another example is illustrated in FIG. 13C. In this case, a pairof waveguides 1332 and 1330 and resonator 1314 are fabricated on thesubstrate in the form of a columnar PBG. The PBG is a uniform array ofcolumns, with the waveguides defined by removing two rows (one for eachwaveguide), and the resonator defined by removing two columns. Top view1333 provides more detail of the construction of waveguides 1330 and1332, and the resonator 1314. Dimensions are dependent on the wavelengthof interest as well as materials used. For a wavelength of 1.55 um, thediameter and spacing of the columns could be on the order of 0.5 um and1 um respectively. The height, h, determines the propagation modes whichwill be supported and should be slightly more than half the wavelengthif only single modes are to be propagated.

[0107] On the inner surface of the membrane 1315 are fabricated twoisolated columns 1311, which are directed downwards, and have the samedimensions and are of the same material (or optically equivalent) as thecolumns on the substrate. The resonator and columns are designed tocomplement each other; there is a corresponding absence of a column inthe resonator where the column on the membrane is positioned.

[0108] When the IMod is in an undriven state, there is a finite verticalairgap 1312, of at least several hundred nanometers between the PBG andthe membrane columns and therefore no optical interaction occurs. Theabsence of columns in the resonator act like defects, causing couplingbetween waveguides 1330 and 1332. In this state the device acts as doesthe one shown in FIG. 13B and selected frequencies of light propagatingalong waveguide are now injected into waveguide 1332, and propagate inthe opposite direction in the form of light 1329.

[0109] Driving the IMod into contact with the PBG, however, places thecolumns into the resonator altering its behavior. The defects of theresonator are eliminated by the placement of the membrane columns. Thedevice in this state acts as does the one shown in FIG. 13A, with light1328 propagating without interference.

[0110] A static version of this geometry is described in the paper H. A.Haus “Channel drop filters in photonic crystals”, Optics Express, vol.3, no. 1, 1998.

Optical Switches

[0111] In FIG. 14A, a device based on the induced absorber includes aself-supporting aluminum membrane 1400, on the order of tens to hundredsof microns square, which is suspended over a stack of materials 1402comprising a combination of metals and oxides and patterned ontransparent substrate. The films utilized in the induced absorbermodulator, described in U.S. patent application Ser. No. 08/688,710,filed on Jul. 31, 1996, and incorporated by reference, could serve thispurpose. The films on the substrate may also comprise a transparentconductor, such as ITO. The structure may incorporate on its underside alossy metal film such as molybdenum or tungsten, of several hundredangstroms in thickness.

[0112] The materials are configured so that in the undriven state thedevice reflects in a particular wavelength region, but becomes veryabsorbing when the membrane is driven into contact. Side view 1410 showsa view of the device looking into the side of the substrate. Light beam1408 propagates at some arbitrary angle through the substrate and isincident on IMod 1406, shown in the un-driven state. Assuming thefrequency of the light corresponds with the reflective region of theIMod in the un-driven state, the light is reflected at a complementaryangle and propagates away. Side view, 1414, shows the same IMod in thedriven state. Because the device is now very absorbing, the light whichis incident upon it is no longer reflected but absorbed by the materialsin the IMod's stack.

[0113] Thus, in this configuration, the IMod may act as an opticalswitch for light that is propagating within the substrate upon which itis fabricated. The substrate is machined to form surfaces that arehighly polished, highly parallel (to within {fraction (1/10)} of awavelength of the light of interest), and many times thicker (at leasthundreds of microns) than the wavelength of light. This allows thesubstrate to act as a substrate/waveguide in that light beams propagatein a direction which is, on average, parallel to the substrate butundergo multiple reflections from one surface to another. Light waves insuch a structure are often referred to as substrate guided waves.

[0114]FIG. 14B shows a variation on this theme. Membrane 1420 ispatterned such that it is no longer rectangular but is tapered towardsone end. While the mechanical spring constant of the structure remainsconstant along this length, electrode area decreases. Thus the amount offorce which can be applied electrostatically is lower at the narrowerend of the taper. If a gradually increasing voltage is applied, themembrane will begin to actuate at the wider end first and actuation willprogress along arrow 1428 as the voltage increases.

[0115] To incident light, the IMod operates as an absorbing region whosearea depends on the value of the applied voltage. Side view 1434 showsthe effect on a substrate propagating beam when no voltage is applied.The corresponding reflective area 1429, which shows the IMod from theperspective of the incident beam, shows “footprint” 1431 of the beamsuperimposed on the reflective area. Since the entire area 1429 isnon-absorbing, beam, 1430, is reflected from IMod 1428 (with minimallosses) in the form of beam 1432.

[0116] In side view 1436, an interim voltage value is applied and thereflected beam 1440 has been attenuated to some extent because thereflective area, shown in 1437 is now partially absorbing. Views 1438and 1429 reveal the result of full actuation and the completeattenuation of the beam.

[0117] Thus, by using a tapered geometry a variable optical attenuatormay be created, the response of which is directly related to the valueof the applied voltage.

[0118] Another kind of optical switch is illustrated in FIG. 15A.Support frame 1500 is fabricated from a metal, such as aluminum severalthousand angstroms in thickness, in such a way that it is electricallyconnected to mirror 1502. Mirror 1502 resides on transparent opticalstandoff 1501, which is bonded to support 1500. Mirror 1502 may comprisea single metal film or combinations of metals, oxides, andsemiconducting films.

[0119] The standoff is fabricated from a material that has the same orhigher index of refraction than that of the substrate. This could beSiO2 (same index) or a polymer whose index can be varied. The standoffis machined so that the mirror is supported at an angle of 45 degrees.Machining of the standoff can be accomplished using a technique known asanalog lithography that relies on a photomask whose features arecontinuously variable in terms of their optical density. By appropriatevariation of this density on a particular feature, three-dimensionalshapes can be formed in photoresist that is exposed using this mask. Theshape can then be transferred into other materials via reactive ionetching. The entire assembly is suspended over conductor, 1503, whichhas been patterned to provide an unobstructed “window” 1505 into theunderlying substrate, 1504. That is to say the bulk of conductor 1503has been etched away so that window 1505, comprising bare glass, isexposed. The switch, like other IMods, can be actuated to drive thewhole assembly into contact with the substrate/waveguide. Side view,1512, shows the optical behavior. Beam 1510 is propagating within thesubstrate at an angle 45 degrees from normal that prevents it frompropagating beyond the boundaries of the substrate. This is because 45degrees is above the angle known as the critical angle, which allows thebeam to be reflected with minimal or no losses at the interface 1519between the substrate and the outside medium by the principle of totalinternal reflection (TIR).

[0120] The principle of TIR depends on Snell's law, but a basicrequirement is that the medium outside the substrate have an index ofrefraction that is lower than that of the substrate. In side view, 1512,the device is shown with the switch 1506 in the un-driven state, andbeam 1510 propagating in an unimpeded fashion. When switch 1506 isactuated into contact with the substrate as shown in side view 1514, thebeam's path is altered. Because the standoff has a refractive indexgreater than or equal to that of the substrate, the beam no longerundergoes TIR at the interface. The beam propagates out of the substrateinto the optical standoff, where it is reflected by the mirror. Themirror is angled, at 45 degrees, such that the reflected beam is nowtraveling at an angle which is normal to the plane of the substrate. Theresult is that the light may propagate through the substrate interfacebecause it no longer meets the criteria for TIR, and can be captured bya fiber coupler 1520, which has been mounted on the opposite side of thesubstrate/waveguide. A similar concept is described in the paper, X.Zhou, et al, “Waveguide Panel Display Using Electromechanical SpatialModulators”, SID Digest, vol. XXIX, 1998. This particular device wasdesigned for emissive display applications. The mirror may also beimplemented in the form of a reflecting grating, which may be etchedinto the surface of the standoff using conventional patterningtechniques. This approach, however, exhibits wavelength dependence andlosses due to multiple diffraction orders that are not an issue withthin film mirrors. Additionally, alternative optical structures may besubstituted for the mirror as well with their respective attributes andshortcomings. These can be categorized as refractive, reflective, anddiffractive and can include micro-lenses (both transmissive andreflective), concave or convex mirrors, diffractive optical elements,holographic optical elements, prisms, and any other form of opticalelement which can be created using micro-fabrication techniques. In thecase where an alternative optical element is used, the standoff and theangle it imparts to the optic may not be necessary depending on thenature of the micro-optic.

[0121] This variation on the IMod acts as a de-coupling switch forlight. Broadband radiation, or specific frequencies if the mirror isdesigned correctly, can be coupled out of the substrate/waveguide atwill. Side view 1526 shows a more elaborate implementation in which anadditional fixed mirror, angled at 45 degrees, has been fabricated onthe side of the substrate opposite that of the de-coupling switch. Thismirror differs from the switch in that it cannot be actuated. By carefulselection of the angles of the mirrors on both structures, light 1522that has been effectively decoupled out of the substrate by switch 1506may be re-coupled back into the substrate by re-coupling mirror 1528.However, by fabricating the re-coupling mirror with differentorientations in the XY plane, the mirror combination may be used toredirect light in any new direction within the substrate/waveguide. Thecombination of these two structures will be referred to as a directionalswitch. The coupling mirrors can also be used to couple any light thatis propagating into the substrate in a direction normal to the surface.

[0122]FIG. 15B shows one implementation of an array of directionalswitches. Looking down onto the substrate 1535, linear array 1536 is anarray of fiber couplers which directs light into the substrate at anangle normal to the XY plane. An array of re-coupling mirrors (notvisible) is positioned directly opposite the fiber coupler array tocouple light into the substrate parallel to beam 1530. On the surfacesof the substrate, 1535, are fabricated an array of directional switchesof which 1531 is one. The switches are positioned in a way such thatlight coupled into the substrate from any one of the input fibercouplers 1536 may be directed to any one of the output fiber couplers1532. In this way the device may act as an N×N optical switch that canswitch any one of any number of different inputs to any one of anynumber of different outputs.

Tunable Filter

[0123] Returning to FIG. 16, an IMod in the form of a tunableFabry-Perot filter is shown. In this case, conducting contact pad 1602has been deposited and patterned along with dielectric mirrors 1604 and1608 and sacrificial layer 1606. This may consist of a silicon film witha thickness of some multiple of one-half a wavelength. The mirrors maycomprise stacks of materials, TiO2 (high index) and SiO2 (low index)being two examples, with alternating high and low in dices, and one ofthe layers may also be air. Insulating layer 1610 is deposited andpatterned such that second contact pad 1612 only contacts mirror 1608.Mirror, 1608 is subsequently patterned leaving a mirror “island” 1614connected by supports 1615. The lateral dimensions of the island areprimarily determined by the size of light beam with which it willinteract. This is usually on the order of tens to several hundredmicrons. Sacrificial layer 1606 is partially etched chemically, butleaving standoffs of sufficient size to provide mechanical stability,probably on the order of tens of microns square. If the top layer ofmirror 1608 and the bottom layer of mirror 1604 are lightly doped to beconducting, then application of a voltage between contact pads 1602 and1612 will cause the mirror island to be displaced. Thus, the structure'soptical response may be tuned.

[0124]FIG. 17A shows an application of this tunable filter. On the topsurface of substrate 1714 has been fabricated tunable filter 1704,mirrors 1716, and anti-reflection coating 1712. A mirror 1717 has alsobeen fabricated on the bottom surface of the substrate, e.g., from ametal such as gold of at least 100 nm thick. Mounted on the top surfaceof the substrate is an optical superstructure, 1706, whose inner surfaceis at least 95% reflective, e.g., by the addition of a reflecting goldfilm, and which also supports an angled mirror, 1710. In this device,light beam 1702 propagates within the substrate at some angle that islarger than the critical angle, which is approximately 41 degrees for asubstrate of glass and a medium of air. Therefore the mirrors 1716 arerequired to keep it bounded within the confines of thesubstrate/waveguide. This configuration allows greater flexibility inthe selection of angles at which the light propagates.

[0125] Beam 1702 is incident upon Fabry-Perot 1704, which transmits aparticular frequency of light 1708 while reflecting the rest 1709. Thetransmitted frequency is incident onto and reflected from the reflectivesuperstructure 1706, and is reflected again by mirror 1716 onto angledmirror 1710. Mirror 1710 is tilted such that the light is directedtowards antireflection coating 1712 at a normal angle with respect tothe substrate, and passes through and into the external medium. Thedevice as a whole thus acts as a wavelength selective filter.

[0126] The superstructure may be fabricated using a number oftechniques. One would include the bulk micromachining of a slab ofsilicon to form a cavity of precise depth, e.g., on the order of thethickness of the substrate and at least several hundred microns. Theangled mirror is fabricated after cavity etch, and the entire assemblyis bonded to the substrate, glass for example, using any one of manysilicon/glass bonding techniques.

[0127]FIG. 17B is a more elaborate version. In this example, a secondtunable filter 1739 has been added to provide an additional frequencyselection channel. That is to say that two separate frequencies may nowbe selected independently. Detectors 1738 have also been added to allowfor a higher degree of integrated functionality.

[0128]FIG. 17C incorporates integrated circuits. Light beam 1750 hasbeen coupled into substrate 1770 and is incident upon tunable filter1752. This filter is different than those of FIGS. 17A and 17B in thatit includes recoupling mirror 1756 that has been fabricated on thesurface of the movable mirror of the filter. The angle of the mirror issuch that the frequency selected by filter 1752 is now coupled directlyback into the substrate at a normal angle in the form of light beam1758. The remaining frequencies contained in light beam 1750 propagateuntil they encounter recoupling mirror 1760 which is angled so that itpresents a surface which is perpendicular to propagating beam 1756. Thebeam thus retraces its path back out of the device where it may be usedby other devices that are connected optically. Light beam 1758 isincident on IC 1764 that can detect and decode the information withinthis beam. This IC may be in the form of an FPGA or other silicon,silicon/germanium, or gallium aresenide device based integrated circuitthat could benefit from being directly coupled to information carryinglight. For example, a high bandwidth optical interconnect may be formedbetween ICs 1764 and 1762 by virtue of the bidirectional light path1772. This is formed by a combination of mirrors 1766 and recouplingmirrors 1768. Light can be emmitted by either ICs if they incorporatecomponents such as vertical cavity surface emitting lasers (VCSELS) orlight emitting diodes LEDs. Light can be detected by any number ofoptically sensitive components, with the nature of the componentdepending on the semiconductor technology used to fabricate the IC.Light that is incident on the IC may also be modulated by IMods thathave been fabricated on the surface of the IC that is exposed to thesubstrate propagating light.

Optical Mixer Using Substrate Waveguide

[0129]FIGS. 18A and 18B are an illustration of a two-channel opticalmixer implemented using a TIR version of a substrate/waveguide. FIG. 18Ashows a schematic of the device. Light containing multiple wavelengthshas two particular wavelengths, 1801 and 1803, split off and directedtowards two independent variable attentuators 1805. They are then outputto several possible channels 1807 or into an optical stop 1813.

[0130]FIG. 18B reveals an implementation. The input light is directedinto the device through fiber coupler 1800, through anti-reflectioncoating 1802, and coupled into the substrate using re-coupling mirror1806. The recoupling mirror directs the light onto tunable filter 1808,splitting off frequency λ1 (beam 1815) and all non-selected frequenciesare directed toward a second tunable filter 1809, which splits offfrequency λ2 (beam 1817), with the remaining frequencies, beam 1819,propagating further downstream via TIR. Following the path of beam 1815,which was transmitted by tunable filter 1808, the light is redirectedback into the substrate waveguide via mirror 1810, through an ARcoating, and re-coupled back into the substrate. The re-coupling mirror1811 directs beam 1815 towards attenuator 1812 where it continues alonga parallel path with beam 1817 selected by the second tunable filter1809. These two beams are positionally shifted by virtue of beamrepositioner 1816.

[0131] This structure produces the same result as a recoupling mirror,except that the mirror is parallel to the surface of the substrate.Because the mirror is suspended a fixed distance beyond the substratesurface, the position of the point of incidence on the oppositesubstrate interface is shifted towards the right. This shift is directlydetermined by the height of the repositioner. The beam 1819, containingthe unselected wavelengths, is also shifted by virtue of repositioner1818. The result is that all three beams are equally separated when theyare incident on an array of decoupling switches 1820 and 1824. Theseserve selectively to redirect the beams into one of two opticalcombiners, 1828 being one of them or into detector/absorber 1830. Theoptical combiners may be fabricated using a variety of techniques. Apolymeric film patterned into the form of a pillar with its top formedinto a lens using reactive ion etching is one approach. Theabsorber/detector, comprising a semiconductor device that has beenbonded to the substrate, serves to allow the measurement of the outputpower of the mixer. Optical superstructures 1829 support externaloptical components and provide a hermetic package for the mixer.

[0132] The combination of planar IMods and a substrate waveguide providea family of optical devices that are easily fabricated, configured, andcoupled to the outside world because the devices reside on the waveguideand/or on the superstructure and are capable of operating on light whichis propagating within the waveguide, and between the waveguide and thesuperstructure. Because all of the components are fabricated in a planarfashion, economies of scale can be achieved by bulk fabrication overlarge areas, and the different pieces maybe aligned and bonded easilyand precisely. In addition, because all of the active components exhibitactuation in a direction normal to the substrate, they are relativelysimple to fabricate and drive, compared to more elaborate non-planarmirrors and beams. Active electronic components may be bonded to eitherthe superstructure or the substrate/waveguide to increase functionality.Alternatively, active devices may be fabricated as a part of thesuperstructure, particularly if it is a semiconductor such as silicon orgallium arsenide.

Printing Style Fabrication Processes

[0133] Because they are planar and because many of the layers do notrequire semiconducting electrical characteristics that requirespecialized substrates, IMods, as well as many other MEM structures, maytake advantage of manufacturing techniques which are akin to those ofthe printing industry. These kinds of processes typically involve a“substrate” which is flexible and in the form of a continuous sheet ofsay paper or plastic. Referred to as web fed processes, they usuallyinvolve a continuous roll of the substrate material which is fed into aseries of tools, each of which selectively coats the substrate with inkin order to sequentially build up a full color graphical image. Suchprocesses are of interest due to the high speeds with which product canbe produced.

[0134]FIG. 19 is a representation of such a sequence applied to thefabrication of a single IMod and, by extension, to the fabrication ofarrays of IMods or other microelectromechanical structures. Web source1900 is a roll of the substrate material such as transparent plastic. Arepresentative area 1902 on a section of material from the rollcontains, for the purposes of this description, only a single device.Embossing tool 1904 impresses a pattern of depressions into the plasticsheet. This can be accomplished by a metal master which has theappropriate pattern of protrusions etched on it.

[0135] The metal master is mounted on a drum that is pressed against thesheet with enough pressure to deform the plastic to form thedepressions. View 1906 illustrates this. Coater 1908 deposits thinlayers of material using well known thin film deposition processes, suchas sputtering or evaporation. The result is a stack 1910 of four filmscomprising an oxide, a metal, an oxide, and a sacrificial film. Thesematerials correspond to the induced absorber IMod design. A tool 1912dispenses, cures, and exposes photoresist for patterning these layers.Once the pattern has been defined, the film etching occurs in tool 1914.Alternatively, patterning may be accomplished using a process known aslaser ablation. In this case, a laser is scanned over the material in amanner that allows it to be synchronized with the moving substrate. Thefrequency and power of the laser is such that it can evaporate thematerials of interest to feature sizes that are on the order of microns.The frequency of the laser is tuned so that it only interacts with thematerials on the substrate and not the substrate itself. Because theevaporation occurs so quickly, the substrate is heated only minimally.

[0136] In this device example, all of the films are etched using thesame pattern. This is seen in 1918 where the photoresist has beenstripped away after the application of tool 1916. Tool 1920, is anotherdeposition tool that deposits what will become the structural layer ofthe IMod. Aluminum is one candidate for this layer 1922. This materialmay also include organic materials which exhibit minimal residual stressand which may be deposited using a variety of PVD and PECVD techniques.This layer is subsequently patterned, etched, and stripped ofphotoresist using tools 1924, 1926, and 1928 respectively. Tool 1930 isused to etch away the sacrificial layer. If the layer is silicon, thiscan be accomplished using XeF2, a gas phase etchant used for suchpurposes. The result is the self-supporting membrane structure 1932 thatforms the IMod.

[0137] Packaging of the resulting devices is accomplished by bondingflexible sheet 1933 to the top surface of the substrate sheet. This isalso supplied by a continuous roll 1936 that has been coated with ahermetic film, such as a metal, using coating tool 1934. The two sheetsare joined using bonding tool 1937, to produce the resulting packageddevice 1940.

Stress Measurement

[0138] Residual stress is a factor in the design and fabrication of MEMstructures. In IMods, and other structures in which structural membershave been mechanically released during the fabrication process, theresidual stress determines the resulting geometry of the member.

[0139] The IMod, as an interferometric device, is sensitive tovariations in the resulting geometry of the movable membrane. Thereflected, or in other design cases transmitted, color is a directfunction of the airgap spacing of the cavity. Consequently, variationsin this distance along the length of a cavity can result in unacceptablevariations in color. On the other hand, this property is a useful toolin determining the residual stress of the structure itself, because thevariations in the color can be used to determine the variations anddegree of deformation in the membrane. Knowing the deformed state of anymaterial allows for a determination of the residual stresses in thematerial. Computer modeling programs and algorithms can usetwo-dimensional data on the deformation state to determine this. Thusthe IMod structure can provide a tool for making this assessment.

[0140]FIGS. 20A and 20B show examples of how an IMod may be used in thisfashion. IMods, 2000, and 2002, are shown from the perspective of theside and the bottom (i.e. viewed through the substrate). They are of adouble cantilever and single cantilever form respectively. In this case,the structural material has no residual stresses, and both membranesexhibit no deformation. As viewed through the substrate, the devicesexhibit a uniform color that is determined by the thickness of thespacer layer upon which they were formed. IMods 2004 and 2006 are shownwith a stress gradient that is more compressive on the top than it is onthe bottom. The structural membranes exhibit a deformation as a result,and the bottom view reveals the nature of the color change that wouldresult. For example if color region 2016 were green, then color region2014 might be blue because it is closer to the substrate. Conversely,color region 2018 (shown on the double cantilever) might be red becauseit is farther away. IMods 2008 and 2010 are shown in a state where thestress gradient exhibits higher tensile stress on the top than on thebottom. The structural members are deformed appropriately, and the colorregions change as a result. In this case, region 2020 is red, whileregion 2022 is blue.

[0141] In FIG. 20B, a system is shown which can be used to quickly andaccurately assess the residual stress state of a deposited film. Wafer2030 comprises an array of IMod structures consisting of both single anddouble cantilevered membranes with varying lengths and widths. Thestructural membranes are fabricated from a material whose mechanical andresidual stress properties are well characterized. Many materials arepossible, subject to the limitations of the requisite reflectivity thatcan be quite low given that the IMods in this case are not to be usedfor display purposes. Good candidates would include materials incrystalline form (silicon, aluminum, germanium) which are or can be madecompatible from a fabrication standpoint, exhibit some degree ofreflectivity, and whose mechanical properties can or have beencharacterized to a high degree of accuracy. These “test structures” arefabricated and released so that they are freestanding. If the materialsare without stress, then the structures should exhibit no colorvariations. Should this not be the case, however, then the color statesor color maps may be recorded by use of a high resolution imaging device2034, which can obtain images of high magnification via optical system2032.

[0142] The imaging device is connected to a computer system 2036, uponwhich resides hardware and capable of recording and processing the imagedata. The hardware could comprise readily available high speedprocessing boards to perform numerical calculations at high rates ofspeed. The software may consist of collection routines to collect colorinformation and calculate surface deformations. The core routine woulduse the deformation data to determine the optimal combination of uniformstress and stress gradient across the thickness of the membrane, whichis capable of producing the overall shape.

[0143] One mode of use could be to generate a collection of “virgin”test wafers with detailed records of their non-deposited stress states,to be put away for later use. When the need arises to determine theresidual stress of a deposited film, a test wafer is selected and thefilm is deposited on top of it. The deposited film alters the geometryof the structures and consequently their color maps. Using softwareresident on the computer system, the color maps of the test wafer bothbefore and after may be compared and an accurate assessment of theresidual stress in the deposited film made. The test structures may alsobe designed to be actuated after deposition. Observation of theirbehavior during actuation with the newly deposited films can provideeven more information about the residual stress states as well as thechange in the film properties over many actuation cycles.

[0144] This technique may also be used to determine the stress of filmsas they are being deposited. With appropriate modification of thedeposition system, an optical path may be created allowing the imagingsystem to view the structures and track the change of their color mapsin real time. This would facilitate real-time feedback systems forcontrolling deposition parameters in an attempt to control residualstress in this manner. The software and hardware may “interrogate” thetest wafer on a periodic basis and allow the deposition tool operator toalter conditions as the film grows. Overall this system is superior toother techniques for measuring residual stress, which either rely onelectromechanical actuation alone, or utilize expensive and complexinterferometric systems to measure the deformation of fabricatedstructures. The former suffers from a need to provide drive electronicsto a large array of devices, and inaccuracies in measuring displacementelectronically. The latter is subject to the optical properties of thefilms under observation, and the complexity of the required externaloptics and hardware.

Discontinuous Films

[0145] Another class of materials with interesting properties are filmswhose structure is not homogeneous. These films can occur in severalforms and we shall refer to them collectively as discontinuous films.FIG. 21A illustrates one form of the discontinuous film. Substrate 2100could be a metal, dielectric, or semiconductor, which has had contours2104, 2106, and 2108 etched into its surface. The contours, comprisingindividual structural profiles which should have a height 2110 that issome fraction of the wavelength of light of interest, are etched usingphotolithographic and chemical etching techniques to achieve profileswhich are similar to those illustrated by, 2104 (triangular), 2106,(cylindrical) and 2108 (klopfenstein taper). The effective diameter ofthe base 2102 of any of the individual profiles is also on the order ofthe height of the pattern. While each contour is slightly different,they all share in common the property that as one traverses from theincident into the substrate, the effective index of refraction goesgradually from that of the incident medium, to that of the filmsubstrate 2100 itself. Structures of this type act as superiorantireflection coatings, compared to those made from combinations ofthin films, because they do not suffer as much from angulardependencies. Thus, they remain highly antireflective from a broaderrange of incident angles.

[0146]FIG. 21B reveals a coating 2120 that has been deposited onsubstrate 2122 and could also be of a metal, dielectric, orsemiconductor. The film, in this case, is still in the early stages offormation, somewhere below 1000 angstroms in thickness. During mostdeposition processes, films undergo a gradual nucleation process,forming material localities that grow larger and larger until they beginto join together and, at some point, form a continuous film. 2124 showsa top view of this film. The optical properties of films in the earlystage differ from that of the continuous film. For metals, the filmtends to exhibit higher losses than its continuous equivalent.

[0147]FIG. 21C illustrates a third form of discontinuous film. In thiscase, film 2130 has been deposited on substrate 2132 to a thickness, atleast a thousand angstroms, such that it is considered continuous. Apattern of “subwavelength” (i.e. a diameter smaller than the wavelengthof interest) holes 2134 is produced in the material using techniqueswhich are similar to the self-assembly approach described earlier. Inthis case, the polymer can act as a mask for transferring the etchpattern into the underlying material, and the holes etched usingreactive ion etch techniques. Because the material is continuous, butperforated, it does not act like the early stage film of FIG. 21B.Instead, its optical properties differ from the unetched film in thatincident radiation experiences lower losses and may exhibit transmissionpeaks based on surface plasmons. Additionally, the geometry of the holesas well as the angle of incidence and refractive index of the incidentmedium may be manipulated to control the spectral characteristics of thelight that is transmitted. 2136 shows a top view of this film. Filmssuch as these are described in the paper “Control of opticaltransmission through metals perforated with subwavelength hole arrays”by Tae Jin Kim. While they are regular in structure, they differ fromPBGs.

[0148] All three of these types of discontinuous films are candidatesfor inclusion into an IMod structure. That is to say they could act asone or more of the material films in the static and/or movable portionsof an IMod structure. All three exhibit unique optical properties whichcan be manipulated in ways that rely primarily on the structure andgeometry of the individual film instead of a combination of films withvarying thickness. They can be used in conjunction with otherelectronic, optical, and mechanical elements of an IMod that they couldcomprise. In very simple cases, the optical properties of each of thesefilms may be changed by bringing them into direct contact or closeproximity to other films via surface conduction or optical interference.This can occur by directly altering the conductivity of the film, and/orby altering the effective refractive index of its surrounding medium.Thus more complex optical responses in an individual IMod may beobtained with simpler structures that have less complex fabricationprocesses.

[0149] Other embodiments are within the scope of the following claims:

1. A reflective display comprising an anti-reflection coating on aviewed surface of the display, the anti-reflection coating beingconfigured to increase the contrast ratio of the display.
 2. The displayof claim 1 comprising interferometric modulators.
 3. An arc-lampstructure comprising a monolithic fabrication on a planar substrate, thefabrication comprising deposited thin films and/or a material of thesubstrate, the fabrication including thin film electrodes between whichan arc is to be formed.
 4. A transmissive or reflective display deviceincorporating the arc-lamp structure of claim
 3. 5. A line-at-a-timeelectronic driving method comprising applying a bias voltage to rows (orcolumns) of a device, applying data voltages to the columns (or rows)alternately about a value of the bias voltage, actuation of the deviceoccurring when the difference between the values of the data voltage andthe select voltage is above a first predetermined level, release of thedevice occurring when the difference between the values of the datavoltage and the select voltage is below a second predetermined levellowest, and the device maintaining its state when the select voltage isat the bias level.
 6. The method of claim 5 in which the devicecomprises multiple MEMS devices.
 7. Apparatus comprising a reflectivedisplay comprising pixel elements each configured to contribute acontrolled amount of white and saturated color, and a controller thatcontrols the pixels to provide a full-color display.
 8. The apparatus ofclaim 7 in which the display comprises interferometric modulators.
 9. Anelectronic product comprising a core non-general-purpose processor thatis reconfigurable to perform any selected one or more of multiplesoftware applications or functions, and a control element that enables auser to reconfigure the processor to use any of the softwareapplications or functions.
 10. The electronic product of claim 9 furthercomprising peripherals, the peripherals being used or reconfigured ormade accessible for interaction based on a configuration of the coreprocessor.
 11. An interferometric modulator comprising a cavity thatprovides for actuation of the modulator, and a separate cavity thatprovides an interference effect.
 12. An interferometric modulatorcomprising a structure associated with actuation of the modulator, andan interferometric cavity having walls, the structure being obscured byat least one of the walls of the interferometric cavity.
 13. Aninterferometric modulator comprising a thin film stack, and a structureassociated with actuation of the modulator, the structure beingdeposited directly upon the thin film stack, interference of thestructure and the stack causing the stack to reflect minimal amounts oflight.
 14. An interferometric modulator comprising a movable wall thatis configured as a spiral by induced residual stresses, in one mode ofoperation, and is un-rolled to form a plate which actsinterferometrically on light in another mode of operation.
 15. Amonolithic MEM modulator comprising a movable plate that is held on asupporting substrate and is configured to selectively obstruct a path oflight, is movable rotationally, about a hinge, in a plane normal to asurface of the supporting substrate, and is actuated by electrostaticforces applied between it and electrodes at the surface of thesubstrate.
 16. The modulator of claim 15 wherein colors or dark statesare imparted by the interferometric properties of thin film stacksdeposited on the modulator structure.
 17. A micromechanical switchcomprising a supporting substrate, and a movable component that effectsswitching by motion in a plane parallel to a plane of the substrate. 18.The switch of claim 17 wherein the movable component provides electricalcontact between a source and a drain.
 19. The switch of claim 17 whereinthe movable component includes an insulating element.
 20. A voltageswitching or logic component that includes the switch of claim
 17. 21.An electronic or MEMS-based device that incorporates the voltageswitching or logic component of claim
 20. 22. A dynamic micromechanicalstructure comprising a structure having an index of refraction thatvaries in a periodic fashion along more than one of at least twoorthogonal axis.
 23. A device for processing light comprising themicromechanical structure of claim
 22. 24. The device of claim 23configured to select and/or redirect specific frequencies of light froma waveguide that is propagating multiple light frequencies.
 25. Thedevice of claim 24 wherein a movable portion of the structure isconfigured to introduce a defect into a periodic photonic structure. 26.The device of claim 24 wherein the movable portion of the structure isconfigured to move a multi-dimensional photonic structure to changeoverall optical properties of the device.
 27. A process for fabricatingmulti-dimensional photonic structures in conjunction withmicroelectromechanical structures, the process comprising holographicpatterning or polymeric self-assembly processes or self-organizingparticle suspensions.
 28. A process for introducing defects intomultidimensional photonic structures, the process comprising using abeam of atomic or sub-atomic particles to modify part of the photonicstructure, by the addition or removal of material, by alteration ofoptical properties of a material or, by using micro-electrodeposition toadd material.
 29. A process for introducing defects into amultidimensional photonic structure, the process forming features onsurface of a substrate, the features configured to provide locations fordevelopment of defects in a later formed photonic structure.
 30. Adevice comprising a substrate, an interferometric modulator fabricatedon the substrate, the interferometric modulator configured to modulatelight propagating within the substrate upon which it is fabricated, in adirection that is generally parallel to the surface of the substrate.31. A device comprising a substrate and a metallic MEM structure formedon the substrate, the MEM structure being configured to modulate lightthat is propagating as guided waves.
 32. The modulator of claims 30 and31 configured to function as a variable attenuator.
 33. A dynamicmicromechanical structure comprising a substrate, and a reflecting opticon the substrate, the reflecting optic when actuated, re-directing lightwhich is incident upon it and is propagating within the substrate,towards another optical structure.
 34. A static microfabricatedstructure comprising a substrate and a mirror fabricated on or in closeproximity to the substrate, the mirror being configured to redirectlight that is incident upon it and is propagating within the substrate.35. An optical switch comprising a dynamic micromechanical structurecomprising a reflecting optic and a fixed microstructure incorporating areflecting optic, the two structures being fabricated on opposite sidesof a substrate/waveguide, the reflecting optics being oriented such thatwhen a beam of light propagating within the substrate/waveguide isincident upon the dynamic structure in an actuated state, the opticalpath of the combined reflecting optics allows the path of the light'spropagation within the substrate/waveguide to be altered arbitrarily.36. The device of claim 34 wherein the reflecting optic comprises amirror.
 37. The device of claim 33 configured to couple light into orout of the substrate.
 38. An optical device comprising micromechanicalstructures configured to process light is propagating within asubstrate/waveguide, and an optical or electronic device configured tothereafter intercept or manipulate the light.
 39. An optical device ofclaim 37 further comprising anti-reflection coatings configured tocouple and decouple light into and out of the substrate/waveguide. 40.The optical device of claim 38 further comprising an opticalsuperstructure that is capable of supporting a combination of staticmicrofabricated components, dynamic micromechanical components, andelectronic components, and that is attached to the substrate/waveguide.41. An optical path repositioning device comprising a patterned block ofdielectric material deposited upon the surface of a substrate/waveguide.42. The device of claim 37 wherein the micromechanical structurescomprise a tunable filter.
 43. An N×N optical switch comprising thedevices of claims 33, 34, or
 37. 44. A wavelength selective switchcomprising the devices of claims 33, 34, or
 37. 45. An optical mixercomprising the devices of claims 33, 34, and
 37. 46. A process forfabricating micromechanical structures comprising feeding a continuousweb of a plastic supporting substrate through a series of tools fordepositing, patterning, and etching deposited films.
 47. A method ofmeasuring a residual stress of deposited materials that comprise aninterferometric cavity which is deformed by the deposition of thematerials to be measured, the method comprising determining thedeformation of the microstructure by measuring a pattern of wavelengthsof light reflected by the cavity.
 48. The method of claim 44 furthercomprising automatically determining the stress of the depositedmaterials based upon the patterns of reflected light.
 49. The method ofclaim 45 further comprising determining the residual stress of filmsduring and after deposition.
 50. A dynamic micromechanical structurecomprising a a dielectric, metallic, or semiconducting film which isdiscontinuous, the optical properties of said film differing from thoseof a continuous film because of the discontinuity.
 51. A dynamicmicromechanical structure comprising a a dielectric, metallic, orsemiconducting film which has been etched in such a way as to produce acontinuous variation in the optical properties of the film through itsdepth.